Optoelectronic transmitter module and method for the production thereof

ABSTRACT

The invention relates to an optoelectronic emission module comprising a housing (B), which has electrical terminal contacts ( 5 ) for supplying and/or carrying away electric signals or for supplying electrical power. Said emission module also has at least one optical emission element ( 13 ), which is arranged inside the housing ( 3 ), and has at least one optical waveguide ( 17 ), which is held inside or on the housing ( 3 ) and in whose injection end ( 19 ) the light emitted by the at least one optical emission element ( 13 ) can be injected. The at least one optical emission element ( 13 ) and the injection end ( 19 ) of the at least one optical waveguide ( 17 ) are mounted on a supporting element. The invention also relates to a method for producing an emission module of the aforementioned type.

[0001] The invention concerns an optoelectronic transmitter modulehaving the characteristics of the generic concept of claim 1 as well asa method for the production thereof according to claim 12.

[0002] Optoelectronic transmitter modules, particularly laser modules,generally include a housing in which, besides the actual opticaltransmitter element, e.g., the laser chip or a LED chip, at least partof the control circuitry is contained. Mechanically and thermally stablecoupling of the optical transmitter element to an optical waveguide isachieved by rigidly connecting a pigtail to the housing. To do this, thecoupling end of the optical waveguide is guided into the housing andpositioned with its front surface in front of the optical transmitterelement so as to achieve optimum coupling efficiency. A design of thissort is used, for example, in pump laser modules, a cylindrical lensbeing formed preferably on the front surface of the coupling end.

[0003] The coupling end is held in a metal ferrule which duringinstallation of the laser module in the housing is adjusted using anautomatic adjustment tool in front of the laser chip previouslyinstalled therein until optimum coupling efficiency is achieved. Once itis optimally positioned, the metal ferrule is fastened using a laserwelding process and a retaining element.

[0004] The retaining element is designed with a saddle shape; twosaddle-shaped bends enclose the metal ferrule on the coupling end andtwo supporting surfaces that are outwardly turned in a perpendicularmanner abut on the floor of the housing. The supporting surfaces arewelded to the housing floor for mounting of the coupling end afterreaching the optimum position and then the metal ferrule to theretaining part with its saddle-shaped design.

[0005] One disadvantage of an optoelectronic transmitter module of thissort is that the entire installation of the individual module elementsmust take place in the housing. This necessitates in particular apositioning tool that is costly to build for positioning the metalferrule in which the coupling end of the optical waveguide is embedded.Moreover, the welding of the retaining part and the metal ferrule to thehousing must take place in the housing itself, which entails significantdifficulties due to the relatively limited space in the housing. Inaddition, in practical terms only the top side or rather the upperlateral regions of the metal ferrule are accessible for the weldingprocedure. Additionally welding the lower regions or rather the bottomside of the metal ferrule in order to achieve the most stable retentionof the ferrule possible is thus very difficult.

[0006] A further problem associated with laser transmitter modules builtin this manner is related to the hermetic sealing of the feedthrough ofthe pigtail through the housing. There is hardly any way to dispensewith a hermetic seal, particularly since otherwise there is a risk thatthe coupling efficiency between the optical transmitter element and thecoupling end of the optical waveguide can be impaired by ambientinfluences, particularly humidity.

[0007] Moreover, optoelectronic transmitter modules are known in whichthe optical transmitter element is arranged in a hermetically sealedhousing, the light from the transmitter element emanating from thehousing through a hermetically sealed window provided in the housing. Onthe outside of the housing, again the front side of the coupling end ofthe optical waveguide is fastened in a position in which optimumcoupling efficiency is ensured. A disadvantage of this design is thecost of the necessary coupling optics between the light-emitting surfaceof the optical transmitter element and the front side of the couplingend of the optical waveguide positioned outside of the housing.

[0008] Based on the prior art described above, the underlying object ofthe invention is to create an optoelectronic transmitter module whichhas a design that is simple and simultaneously easy to install, it beingpossible to simultaneously guarantee the necessary mechanical andthermal stability as well as the long-term stability of the transmittermodule. Moreover, the underlying object of the invention is to create amanufacturing technique for an optoelectronic transmitter module of thissort that guarantees that the transmitter module can be installed in thesimplest and most cost-effective manner.

[0009] This objective is solved by the invention with the features ofclaim 1 or rather claim 12.

[0010] By arranging at least one optical transmitter element andfastening the coupling end of at least one optical waveguide on a commonsupporting element, the advantage ensues that this submodule can beassembled and checked and subjected to a burn-in test outside of thehousing. Assembly outside of the housing simplifies the requiredprocedural steps, particularly the positioning and fastening of thecoupling end of the optical waveguide.

[0011] Moreover, the advantage is achieved that only functionalsubmodules are installed in a housing. Whereas in known transmittermodules, the assembly takes place in the housing and if a proceduralstep fails, the entire previously assembled module including the housingmust be rejected and discarded, in the transmitter module or rathermanufacturing technique according to the invention, the possibilityexists to reject and discard only the affected part of the submoduleproduced outside of the housing. Since housings, and particularlyhousings having a Peltier element already integrated or rather installedin them, generate a significant share of the costs of a completedtransmitter module, a corresponding cost benefit ensues from theproduction of transmitter modules according to the invention.

[0012] According to the preferred embodiment of the invention, thecommon supporting element is made of a material with good heatconductivity, such as wolfram copper. In this manner, the supportingelement can effectively convey the heat produced by the opticaltransmitter element or rather the control circuitry to the housing orrather to the Peltier element arranged below the supporting element.

[0013] According to the preferred embodiment of the invention, theoptical transmitter element and the control circuitry including therequired current paths or rather conductor tracks is [are] arranged on asubstrate. The substrate can be made of, say, ceramics or silicon. Inone embodiment of the invention, the optical waveguide end is held in apositioning and fastening element which has a stopping face for axiallypositioning the front side of the optical waveguide end, which stoppingface cooperates with a stopping face formed on the supporting element.This results in the advantage that following precise cutting of thecoupling end of the optical waveguide with respect to the stopping faceof the positioning and fastening element, axial alignment of thecoupling end can be eliminated.

[0014] In one embodiment of the invention, the positioning and fasteningelement includes a ferrule which can be made of glass or metal in whichthe coupling end is held, e.g., cemented into place. The stopping facefor the axial positioning can be formed on the outer circumference ofthe ferrule.

[0015] According to the preferred embodiment of the invention, thepositioning and fastening element includes a receptacle part whichdefines the stopping face for the axial positioning and which has arecess or rather bore hole in which the ferrule is held, preferablypressed in.

[0016] This results in a fastening for the coupling end which ismechanically and thermally stable over the long term.

[0017] According to another embodiment of the invention, the couplingend of at least one optical waveguide can be arranged directly on thesubstrate in front of the light-emitting surface of at least one opticaltransmitter element. For this purpose, at least one V groove can beformed in the substrate to receive and position the coupling end. Here,it is advantageous that fast and simple positioning of the coupling endcan be guaranteed. However, a prerequisite for this is the precisepositioning of the optical transmitter element on the substrate as wellas the highly precise manufacture of the V groove(s).

[0018] Naturally, positioning of at least one coupling end using Vgrooves can be applied even when using a positioning and fasteningelement. Instead of a ferrule, here, the coupling end is inserteddirectly into the relevant V groove and fastened, e.g., applied with afastening element (e.g., a plate) and/or cemented.

[0019] According to the preferred embodiment of the invention, couplingoptics between the light-emitting surface of at least one opticaltransmitter element and the front surface of the relevant coupling endare eliminated. This applies also to a lens-shaped formation of thefront surface of the coupling end. In this manner, according to thepreferred embodiment of the invention, at least the space between theemitting surface of the optical transmitter element and the frontsurface of the coupling end can be filled with a transparent material,preferably a transparent sealing compound. The associated immersion doesnot disadvantageously affect the beam path due to the lack of couplingoptics. Instead, what ensues as a result is the advantage of a reductionin the divergence of the light radiated by the optical transmitterelement and a reduction in the optical power reflected at the boundarysurfaces.

[0020] In order to make do without coupling optics, a semiconductorlaser chip is preferably used as the optical transmitter element; such asemiconductor laser chip has spot broadening integrated in the chip bymeans of a taper structure (taper laser). As a result of the spotbroadening, the emitting surface of the laser is matched to the spotradius of the optical waveguide. The divergence of the radiated light issimultaneously reduced and also matched to the numerical aperture of theoptical waveguide.

[0021] If a sealing compound with long-term mechanical stability ischosen as the transparent material, this results in the advantage of asort of encapsulation of the coupling region between the opticaltransmitter element and the coupling end. Thus, in a transmitter moduleaccording to the invention, a fully hermetic seal of the housing can beeliminated. This makes it possible, for example, to feedf the opticalwaveguide through the housing wall simply by bonding the opticalwaveguide and by providing suitable mechanical stabilization of theregion of the optical waveguide abutting the outer wall of the housing.This results in a simple and cost-effective construction of thetransmitter module.

[0022] Further embodiments of the invention are provided by thedependent claims.

[0023] The invention is explained in greater detail hereafter based onembodiments shown in the drawings. The figures are as follows:

[0024]FIG. 1: A perspective schematic view of a first embodiment of astill open optical transmitter module according to the invention;

[0025]FIG. 2: A representation similar to FIG. 1 of a second embodimentof a transmitter module according to the invention;

[0026]FIG. 3: A perspective schematic representation of a submoduleproduced outside of the housing of the embodiment in FIG. 2; and

[0027]FIG. 4: A perspective schematic representation of a submodule fora third embodiment of a transmitter module according to the invention.

[0028] The embodiment shown in FIG. 1 of an optoelectronic transmittermodule 1 includes a housing 3 which in the shown embodiment is formed asa butterfly housing. Of course, any other housing type can also be used.The housing 3 has terminal contacts 5 extending in each case laterallyoutwards for supplying and/or carrying away electrical signals or forsupplying electrical power. In the housing 3, a submodule 7 is arrangedwhich includes a supporting element 9. On the supporting element 9, asubstrate 11 is arranged, which can be made of ceramics, for example.The substrate 11 can be cemented to the supporting element 9, forexample, or rigidly connected to it in some other manner.

[0029] On the substrate 11, an optical transmitter element 13 ispreferably arranged so that the light-emitting surface of thetransmitter element 13 terminates essentially flush with an outer sideof the substrate 11. Besides the optical transmitter element 13, whichis preferably formed as a laser chip, particularly a tape laser chip,further components of the electronic controller for the opticaltransmitter element 13 can be arranged on the substrate 11. Of course,this applies also to the track structures for making contact with thecomponents. The contacting of the components arranged on the substrate11 can take place in the conventional manner by means of bonding,corresponding terminal contact surfaces on the substrate 11 beingconnected to terminal contact surfaces provided in the housing of theterminal contacts 5.

[0030] For injection of the light emitted by the optical transmitterelement 13 into the coupling end 19 of an optical waveguide 17 of apigtail 15, the coupling end 19 must be positioned and fastened with itsfront surface exactly in front of the light-emitting surface of theoptical transmitter element 13. For this purpose, in the embodimentshown in FIG. 1 of an optoelectronic transmitter module 1, the couplingend 19 is held in a ferrule 21, e.g., a glass ferrule. The coupling end19 can be cemented for this purpose in the axial drill hole of theferrule 21. The ferrule 21 and a receptacle part 23 form a positioningand fastening element 25 for the coupling end 19.

[0031] The receptacle part 23 can be designed with a ring shape, theferrule 21 being held in the receptacle part 23, preferably pressed in.

[0032] The production of the positioning and fastening element for thecoupling end 19 takes place, as does the arrangement of the substrate 11on the supporting element 9 and the components on the substrate 11,outside of the housing 3. These two subunits, which are also stilloutside the housing, are thus connected together and fastened so thatthe front surface of the coupling end 19 is optimally positioned infront of the light-emitting surface of the optical transmitter element13. The front face of the ring-shaped receptacle part 23 serves as astopping face to position the coupling end 19 in the axial direction infront of the optical transmitter element 13, such that the stopping facecooperates with a corresponding stopping face on the front side of thesupporting element 9. For this purpose, the supporting element 9 has onits front region a U-shape in terms of its cross section, its front sidedefining the relevant stopping face.

[0033] Whereas the rear region of the supporting element 9 on which thesubstrate 11 is arranged is made of a material with good heatconductivity, e.g., copper, the front U-shaped region of the supportingelement 9 can be made of a material which can be easily welded to thering-shaped receptacle part 23. A possible material for the U-shapedregion and the receptacle part 23 is, say, covar. The joining of theU-shaped front region of the supporting element 9 to its rear region cantake place, say, through soldering or welding.

[0034] The manufacture of the positioning and fastening element 25 takesplace such that the front surface of the coupling end 19 of the opticalwaveguide 17 has a precisely defined spacing from the stopping face ofthe receptacle part 23. This can take place, for example, in that thecoupling end 19 is precisely cut following the joining of the parts ofthe positioning and fastening element 25. This can take place, forexample, through laser detachment of the coupling end 19.

[0035] Thus, no adjustment procedure is required on the coupling end 19in terms of its axial direction. Only an adjustment of the coupling end19 in the two transverse axes, i.e., in the radial direction, isrequired. The adjustment of the positioning and fastening element 25with respect to the light-emitting surface of the optical transmitterelement 13 can also take place, as was already described, outside of thehousing 3. The adjustment procedure is carried out preferably using anautomatic adjustment tool. For example, the adjustment can take placesuch that the optical transmitter element 13 is triggered and theoptical power coupled into the coupling end 19 at the end of the opticalwaveguide 17 of the pigtail 15 is detected. In the position at whichmaximum transmission occurs (upon abutment of the stopping face of thereceptacle part 23 and of the supporting element 9), this optimumposition is then fixed through laser welding of the receptacle part 23to the U-shaped region of the supporting element 9.

[0036] Since the welding of these two parts takes place outside of thehousing so that these parts are accessible over the entire perimeter,two welding points U 27 can be set, for example, in the upper region ofthe U legs of the supporting element 9 and a third welding point (notshown) in the middle level of the submodule 7 in the lower region of thereceptacle part 23 or rather of the U-shaped region of the supportingelement 9. This results in a three-point welding joint with long-termmechanical stability.

[0037] Following the manufacture of the submodule 7, it can be subjectedto further tests or rather to a burn-in test.

[0038] Installation in the housing 3 does not take place until it hasbeen ensured that the submodule is fully functional in the desiredmanner. For this purpose, the pigtail 15 is pulled through a drill hole29 in the housing 3, the drill hole 29 extending also through acylindrical prolongation 31 which is provided on the outer wall of thehousing 3. Then, the submodule 7 with the underside of the supportingelement 19 is joined (e.g., cemented) to the housing floor or a Peltierelement already arranged in the housing.

[0039] Then, the pigtail 15 is cemented in the drill hole 29 of thehousing 3 and the feedthrough of the pigtail 15 is sealed off in thismanner. Then, a mechanical fastening of the pigtail is normally applied,e.g., in the form of a heat-shrinkable sleeve or the like.

[0040] In a final step, the housing is sealed by applying a cover (notshown).

[0041] The embodiment of an optoelectronic transmitter module 1 shown inFIG. 2 corresponds essentially to the embodiment shown in FIG. 1. Itdiffers, however, in that the pigtail 15 includes four opticalwaveguides instead of a single optical waveguide. Moreover, the opticaltransmitter element 13 is a four-way transmitter element. For thispurpose, a single chip can include multiple lasers which in turn aredesigned essentially identically. The submodule 7 of the embodimentshown in FIG. 2 is shown in isolation in FIG. 3. As can be seen in FIG.3, the receptacle part 23 is designed as an essentially cylindrical partwhich has a radial indentation of the desired width. In thisindentation, a plate 23 a is held which extends over the front side ofthe receptacle part 23 forming the stopping face in the direction of theoptical transmitter element 13. In the surface of the plate 23 a, fourparallel-running V grooves are formed which are intended to guide andfasten the coupling ends 13 of the optical waveguides 17. The plate 23 acan be cemented or welded to the floor of the indentation of thereceptacle part 23. The fastening of the coupling ends 19 in the Vgrooves of the plate 23 a can take place, for example, in that afastening plate 33 is placed over the coupling ends 19 which fasteningplate 33 the coupling ends 19 act upon with their under side. Thefastening plate 33 can be cemented to the plate 23 a and the couplingends 19.

[0042] After the coupling ends 19 are fastened in the receptacle part23, they can be cut in turn to a defined length referred to the stoppingface of the receptacle part 23.

[0043] The adjustment of the positioning and fastening element 25 formedin this manner with respect to the four light-emitting surfaces of thefour-way optical transmitter element 13 takes place in turn in theradial direction (preferably a first axis in the direction of theconnecting straight lines of the four light-emitting surfaces and asecond axis perpendicular to this) and additionally through rotationabout the longitudinal axis of the receptacle part 23. The adjustmentprocedure takes place analogously to the embodiment described inconjunction with FIG. 1. Of course, two, three or all four lasers can betriggered for the adjustment procedure.

[0044]FIG. 4 shows a submodule 7 in which the supporting element 9 isformed by a substrate on which the optical transmitter element 13 andfurther components for controlling the optical transmitter element 13are arranged, on the one hand, and on the other hand the coupling ends19 are guided and fastened in V grooves already formed on the supportingelement 9. The attachment of the coupling ends 19 can take place againby means of a fastening plate 33 in the previously described manner. Ofcourse, an embodiment of this sort is possible with the four-waytransmitter module shown in FIG. 4b, but it is also suitable for asimple (1-way) module or an n-way module. This also naturally applies tothe embodiment according to FIGS. 2 and 3.

1. An optoelectronic transmitter module having a) a housing (B) whichhas electrical terminal contacts (5) for supplying and/or carrying awayelectric signals or for supplying electrical power, b) at least oneoptical transmitter element (13) which is arranged inside the housing(3), and c) at least one optical waveguide (17) which is held inside oron the housing (3) in whose coupling end (19) the light emitted by atleast one optical transmitter element (13) can be injected,characterized in that d) at least one optical transmitter element (13)and the coupling end (19) of at least one optical waveguide (17) areinstalled on a supporting element.
 2. The transmitter module accordingto claim 1, characterized in that the supporting element (9) is made ofa material with good heat conductivity, such as copper, and is joined tothe housing (3) or a cooling element in a heat-conducting manner.
 3. Thetransmitter module according to claim 1 or 2, characterized in that atleast one optical transmitter element (13) is arranged or formed on asubstrate (11) which is joined to the supporting element (9).
 4. Thetransmitter module according to one of the preceding claims,characterized in that at least one coupling end is held in a positioningand fastening element (25), that the supporting element (9) defines afirst stopping face which cooperates for positioning the coupling end(19) of at least one optical waveguide (17) in the axial direction witha second stopping face which is formed on the positioning and fasteningelement (25).
 5. The transmitter module according to claim 4,characterized in that the positioning and fastening element (25)includes a ferrule (21) in which at least one coupling end (19) is held.6. The transmitter module according to claim 5, characterized in thatthe positioning and fastening element (25) includes a receptacle part(23) which defines the second stopping face and that the ferrule (21) isheld in a drill hole in the receptacle part (23), preferably pressed in.7. The transmitter module according to one of the claims 1 to 4,characterized in that in the positioning and fastening element (25) or apart joined to it at least one V groove is formed for receiving at leastone coupling end (19).
 8. The transmitter module according to claim 1 or2, characterized in that at least one optical transmitter element isarranged on the supporting element (9) and that in the supportingelement (9) at least one V groove is formed for receiving andpositioning at least one coupling end.
 9. The transmitter moduleaccording to one of the preceding claims, characterized in that at leastthe space between the emitting surface of at least one opticaltransmitter element (13) and the front surface of the coupling end (19)associated with this transmitter element is filled with a transparentmaterial, preferably a transparent sealing compound.
 10. The transmittermodule according to one of the preceding claims, characterized in thatthe optical transmitter element (19) is a semiconductor laser chip whichpreferably has spot broadening integrated in the chip by means of ataper structure.
 11. The transmitter module according to claim 10,characterized in that in the coupling end of at least one opticalwaveguide (17), a fiber grating for creating a fiber grating laser isformed.
 12. The transmitter module according to one of the precedingclaims, characterized in that the housing (3) is a non-hermeticallysealed housing.
 13. A method of manufacturing an optical transmitterelement according to one of the preceding claims, characterized in thatthe supporting element (9) with all optical transmitter elements to bearranged thereupon and all coupling ends (19) to be connected thereto isprefabricated into a submodule (7) and that subsequently a functional,prefabricated submodule (7) is installed in a housing (3).